1. Field of the Invention
Generally, the field of the present invention is monitoring the power of light emitted by a laser. More particularly, the present invention relates to an integrating volume for homogenizing a sample of the laser light before the monitoring occurs.
2. Background Art
In many laser-based systems it is desirable to internally monitor the output power of the laser by sampling a small portion of the laser light with a monitor photodiode (MPD). The electrical signal output from the MPD may be used to adjust either the current or voltage in a feedback system for controlling the operation of the laser. One challenge that is faced in being able to effectively monitor the output power of the laser beam is that the detected power is not uniform.
Another issue that often arises when using a MPD is the small signal level that is required to saturate the photodiode response. Most MPD saturate at peak power levels of a few mW, meaning that sufficient attenuation of the pick-off beam taken from the main beam needs to be provided.
To ensure that the MPD spatially samples the entire pick-off beam, it is desirable to homogenize the beam intensity profile. Beam homogenization can be achieved through several methods, such as an engineered diffuser or a classical integrating sphere. Integrating spheres are common optical components used for various lab and industry purposes. The inside of integrating spheres is often made with a highly reflective surface that produces almost perfect Lambertian scatter, meaning that the reflected light from any given surface reflects with equal intensity in all directions (2π steradians).
While in theory integrating spheres can perfectly homogenize a given light source with little optical loss, many are expensive and can be rather large, although a miniaturized integrating sphere is disclosed in U.S. Pat. No. 6,846,085. Furthermore, often integrating spheres cannot handle high peak power applications like those found in diode pumped solid state laser systems or fiber laser systems. Consequently, there remains a need for an innovation that avoids the drawbacks of the integrating sphere.